iv THE CHURCH OF S. IRENE 101
with the springing of the aisle vaulting. Projecting above the ground at the same place is a square mass of stonework that was left unbuilt upon when that rebuilding took place. The narthex is built of brick5 with bands of large stone at wide intervals, and is separated by distinct joints from the upper and lower walls of the body of the church. Furthermore, while the two eastern bays on each side of the western portion of the nave continue and belong to the unusual system of vaulting followed in the aisles, the bay on each side immediately adjoining the narthex belongs to the vaulting system found in the narthex, and has, towards the nave, an arch precisely similar to the arches between the nave and the narthex. The division between the two systems is well marked, both in the nave and in the aisles, and points clearly to the fact that the narthex and the body of the church are of different dates.
Thus the architectural survey of the building shows that the principal parts of the fabric represent work done upon it on three great occasions, a conclusion in striking accord with the information already derived from history. For we have seen (p. 89) that after the destruction of the original Con-stantinian church by fire in the Nika Riot, Justinian the Great erected a new sanctuary upon the old foundations ; that later in his reign another fire occurred which necessitated the reconstruction of the narthex of that sanctuary ; and that some two centuries later, towards the close of the reign of Leo the Isaurian, the church was shaken by one of the most violent earthquakes known in Constantinople, and subsequently restored probably by that emperor or by his son and successor Constantine Copronymus. Accordingly, leaving minor changes out of account, it is safe to suggest that the walls of the body of the church, up to the springing of the aisle vaults, belong to the new church built by Justinian after the Nika Riot in 532 ; while the narthex, the aisle vaults immediately adjoining it, and the upper portion of the western end of the south wall, represent the repairs made probably by the same emperor after the injuries to the fabric caused by the fire of 564. The earthquake of 740 must therefore have shaken down or rendered unstable all the upper part